PSU gurus, what's this?

NightmareXX · 24 Feb 2009 at 23:11

So my PSU recently died after almost 3 years of service. Thankfully, when it did go, nothing went with it

It's out of warranty so being the sort of person who likes to know, I took it apart and seem to have found what I believe to be the culprit.

Orientation as seen from the main power cable in

Orientation as seen from the PC output cables

Failed component

Area around failed component (Note the black charring)

So, any ideas what it is?

Dantoshou · 25 Feb 2009 at 08:35

dont know much about psu's insides, but that looks nice and chargrilled, a transistor or resistor? something along those lines..
gz on reaching 3 years with that thing, <3 the amount of dust ^_^
ive got a little dell dimension thats lasted like 7/8 years and is still going with hell knows what psu lol
are you hoping to replace the part or buy another?

Albaba · 25 Feb 2009 at 09:06

Just snap the burnt bit off should work fine again

IAmATeaf · 25 Feb 2009 at 11:00

It looks like a MOV (Metal Oxide Varistor), they are designed to burn themselves out should there be a problem with the PSU, should be easy enough to get and replace but I see that you cut the leads on the PSU.

NightmareXX · 25 Feb 2009 at 11:57

Yea it's served me long enough and I wouldn't be comfortable with replacing a part on such a critical component. Looks like the part did it's job and prevented my PSU from taking things with it

BullBoyShoes · 25 Feb 2009 at 12:35

as stated above, looks like a varistor. You may have had a power surge, the varsitor goes short circuit and blows the fuse instantly

NightmareXX · 25 Feb 2009 at 12:41

Power surge? That'd be an odd one. The PC is plugged into a surge protector although when I unplugged it and did some testing, I did find that the fuse had blown (5A). Doesn't this mean that the PSU had drawn 5x240 = 1200W?

BullBoyShoes · 25 Feb 2009 at 12:56

well, whatever caused it, the varistor went short and blew the fuse - it did what it was designed to do. You could replace them and see what happens, but after that amount of time I would get a new one

NightmareXX · 25 Feb 2009 at 13:00

Yea I've got a new one arriving today although I still don't quite understand how a surge could have got through and taken it out. A surge to the protector would have also traveled along to my monitor and speakers which are plugged into the same block. Why my PSU and not the monitor or speakers?

If it had overheated, would that have caused the MOV to go?

Cybermyk · 25 Feb 2009 at 13:08

You could possibly have a case with the surge protector manufacturer if it was a power surge. They usually give a lifetime warranty and insurance.

NightmareXX · 25 Feb 2009 at 13:12

Yea, I could do but I've got no proof of a surge nor did it do anything unexpected. I've had the PSU for nearly 3 years, it's been used pretty damn well and I'm not too surprised it went pop.

If it had taken out my monitor, speakers and my entire PC, it'd be a different story entirely.

Sasahara · 25 Feb 2009 at 13:28

The components failing in the PSU probably caused the fuse to blow(as it should), rather than a power surge from the mains supply.

Surge protectors only cover overloads from the mains supply, not overload as a result of a faulty appliance.

IAmATeaf · 25 Feb 2009 at 13:35

Sasahara said:
The components failing in the PSU probably caused the fuse to blow(as it should), rather than a power surge from the mains supply.

Surge protectors only cover overloads from the mains supply, not overload as a result of a faulty appliance.

As above, the MOV's function is to prevent over-volting, so more likely that something went bad in the PSU, the MOV heated, blew and shorted which in turn took the fuse out. Another way you can normally blow the MOVs is to change the switch on the back of the PSU (that's if it has one) to 110 then plug it into 240 mains

Quite safe in this case to do a repair on the PSU as it was user error

EsaT · 25 Feb 2009 at 16:06

That's dust filled FSP/Fortron Epsilon design...
(dust surely won't make good to PSUs)

Marking on PCB seems to start with R so that would hint toward somekind resistor and looks much like MOV. But darkened PCB tells it surely has gotten hot before blowing up... maybe that's why some PSUs of this design have it wrapped inside plastic.

Also some flame has hit main capacitor and that black spot behind "leg" of heatsink looks like it has shorted to something and PSU case is only thing in that direction.
Do you see any signs in casing on there or in plastic insulator which should be between casing and components?

IAmATeaf · 25 Feb 2009 at 19:43

AFAIK they are normally covered in heatshrink as when they go they can quite literally explode, the heatshrink would minimise the damage I suppose.